This invention relates to gain control and analog frequency-selective filtering of electronic signals. In particular, this invention relates to circuits and techniques for controlling gain and filtering a signal in ways which limit the introduction of noise to the signal while operating within reasonable power constraints and employing a minimum amount of die space.
Gain control and analog frequency-selective filtering are typical needs in electronic systems that operate on analog input signals with widely-varying amplitude. This situation arises, for example, in receivers of many kinds (including radio, cable modems, sonar, ultrasound) and in the preprocessing of signal inputs for sampling and analog-to-digital conversion. Electrical noise introduced by the circuitry that performs the gain control and filtering must be minimized since it corrupts the input signal.
A traditional approach to filtering signals with wide amplitude range is to add a separate explicit variable-gain circuit (often called a variable-gain amplifier or programmable-gain-amplifier, VGA or PGA, respectively) in the signal path prior to a filter. This amplifier amplifies small signals so they can be processed by the rest of the circuit. This conventional approach requires additional circuitry for the PGA and the filter (and therefore more power). The additional circuitry also tends to introduce more noise into the signals.
In view of the foregoing, it would be desirable to provide circuits for controlling the gain of electronic signals and filtering electronic signals requiring less components than required by conventional circuits.
It would be further desirable to provide circuits for controlling the gain of electronic signals and filtering electronic signals while reducing the power required by the circuits.
It would be still further desirable to provide circuits for controlling the gain of electronic signals and filtering electronic signals while minimizing the die space required by the circuits.
It would be yet further desirable to provide circuits for controlling the gain of electronic signals and filtering electronic signals while reducing the introduction of electronic noise by the gain control and filtering circuits.